Re: [alsa-devel] [PATCH] ALSA: pcm: prevent UAF in snd_pcm_info

On Tue, Dec 5, 2017 at 11:14 AM, Takashi Iwai tiwai@suse.de wrote:

On Tue, 05 Dec 2017 18:16:55 +0100, Nick Desaulniers wrote:

...

From: Robb Glasser rglasser@google.com

When the device descriptor is closed, the `substream->runtime` pointer is freed. But another thread may be in the ioctl handler, case SNDRV_CTL_IOCTL_PCM_INFO. This case calls snd_pcm_info_user() which calls snd_pcm_info() which accesses the now freed `substream->runtime`.

Signed-off-by: Robb Glasser rglasser@google.com Signed-off-by: Nick Desaulniers ndesaulniers@google.com

Looks reasonable. Applied with Cc to stable now.

FWIW, this was assigned CVE-2017-0861. (Best to get it into the commit log if possible.)

-Kees

thanks,

Takashi

...

---

sound/core/pcm.c | 2 ++ 1 file changed, 2 insertions(+)

diff --git a/sound/core/pcm.c b/sound/core/pcm.c index 9070f277f8db..09ee8c6b9f75 100644 --- a/sound/core/pcm.c +++ b/sound/core/pcm.c @@ -153,7 +153,9 @@ static int snd_pcm_control_ioctl(struct snd_card *card, err = -ENXIO; goto _error; }

•                 mutex_lock(&pcm->open_mutex);
                  err = snd_pcm_info_user(substream, info);
  

•                 mutex_unlock(&pcm->open_mutex);
          _error:
                  mutex_unlock(&register_mutex);
                  return err;
  

-- 2.15.0.531.g2ccb3012c9-goog